Science regularly praises the health benefits or warns us of the dangers of consuming various foods. The same food or beverage may even be both lauded and vilified from one year to the next, and from one study to another (coffee, for example). But the results of the current study are based on data collected from a population of nearly 28,000 men over a period of 20 years. Here’s a summary of the research recently published in Neurology.

Changzheng Yuan and her colleagues at Harvard T.H. Chan School of Public Health wanted to assess the potential link between long term fruit and vegetable consumption and subjective cognitive function (SCF). They followed 27,842 men (all health professionals) with an average age of 51 in 1986. At the beginning of the study, the participants filled out questionnaires on the number of fruit, vegetable and other food servings they ate daily. The questionnaires were then repeated every 4 years for 20 years, until 2002. Note that according to this protocol, a fruit serving was defined as a cup of fruit or half cup of fruit juice, and a vegetable serving was defined as a cup of raw vegetables or two cups of cooked veggies (i.e. spinach or cabbage).

There were large variations among participants, with some reporting six vegetable servings a day, while other reporting only two. This was also true for fruit: those with the lowest consumption reported only half a serving, while fruit-lovers reported three servings a day.

At least four years prior to the end of the protocol, the participants (who were now an average of 73 years old) completed a questionnaire about their thinking and memory skills in order to see if there had been any changes in these functions. They were given six questions, including: "Do you have more difficulty than usual remembering a short shopping list?" Or “Is it harder than usual to follow a group conversation or understand the plot of a TV program?". In total, 55% of participants reported having good thinking and memory skills, 38% moderate, and 7% reported low abilities.

The researchers detailed the following main results:
- The men that consumed the most vegetables were 34% less likely to develop poor thinking skills than those who consumed the least vegetables. - The men who drank orange juice daily were 47% less likely to develop poor thinking skills than those who drank less than one serving per month. This was especially true in the oldest participants.
- The men that ate the most fruit per day were less likely to develop poor thinking skills. But this correlation diminished after taking other products into account, like vegetables, refined grains, and dairy products.
- Men that ate lots of fruits and vegetables at the beginning of the study were less likely to develop thinking and memory problems; and this was true whether or not they continued to consume the same large quantities about six years prior to the memory test.

It’s important to note that this study does not show that consuming fruits, vegetables, and orange juice reduces memory loss. It simply confirms that there is a relationship between the two, and confirms the beneficial role of these foods on SCF.

Finally, the authors mention the two main limitations of their research. The participants' thinking and memory skills were not assessed at the beginning of the study, and the volunteers were all health professionals (dentists, veterinarians, nurses, etc.), making it impossible to generalize the results to the overall population.